Mobile devices such as cellphones commonly contain proximity sensors. These can be used to determine when the user's head is close to the device (e.g., within 5 centimeters of a front face of the device), so that the touch input of a touchscreen display can be deactivated during a call. This can prevent unintended inputs to the device due to contact between the device and the user's head. Such proximity sensors typically emit infrared signals and detect changes in the reflected infrared signal returning to the sensors (e.g., changes in amplitude). Such sensors are simple, but they can significantly increase the bill of materials for the mobile device and take up significant additional space on the face of the device.
The applicant has therefore devised an alternative approach.